The remote delivery of low vapor pressure precursors in solid or liquid form to a process chamber requires heating of an ampoule that holds the low vapor pressure precursor and a long gas line that carries the vaporized low vapor pressure precursor to a process chamber, for example, to expose a substrate to the precursor. However, the heating/isolating of the long gas line is apt to fail and is often difficult to maintain. Moreover, the inventors have observed that remote delivery of the precursor may also have a slow response believed to be due to the line volume and the limited flow rate of the precursor from the ampoule. The inventors have further observed that such heated delivery systems also require an upstream mass flow controller (MFC) to control the gas flow rate in order to avoid any condensation problems inside the MFC. However, positioning the MFC upstream of the ampoule makes the ampoule susceptible to downstream pressure fluctuation, which impacts the delivery accuracy of the precursor.
Thus, the inventors have provided herein improved methods and apparatus for gas delivery of low vapor pressure precursors.